[m-rev.] diff: .NET back-end: fix string__sub_string_search

[Fergus Henderson]

Estimated hours taken: 6
Branches: main

library/string.m:
	Fix a bug in the MC++ definition of string__sub_string_search:
	it was not setting SUCCESS_INDICATOR.
	Also fix a bug in the Mercury definition of string__sub_string_search:
	it was trying to match against the same position (the start of
	the string) at every iteration of the loop.

Workspace: /home/fjh/ws/hermes
Index: library/string.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/string.m,v
retrieving revision 1.190
diff -u -d -r1.190 string.m
--- library/string.m	29 Nov 2002 13:25:56 -0000	1.190
+++ library/string.m	13 Feb 2003 17:19:28 -0000
@@ -463,7 +463,8 @@
 :- mode string__sub_string_search(in, in, out) is semidet.
 %	string__sub_string_search(String, SubString, Index).
 %	`Index' is the position in `String' where the first occurrence of
-%	`SubString' begins.
+%	`SubString' begins.  Indices start at zero, so if `SubString'
+%	is a prefix of `String', this will return Index = 0.
 
 :- func string__format(string, list(string__poly_type)) = string.
 :- pred string__format(string, list(string__poly_type), string).
@@ -1262,25 +1263,35 @@
 	[will_not_call_mercury, promise_pure, thread_safe],
 "{
 	Index = WholeString->IndexOf(SubString);
+	SUCCESS_INDICATOR = (Index >= 0);
 }").
 
+% This is only used if there is no matching foreign_proc definition
 string__sub_string_search(String, SubString, Index) :-
-	sub_string_search_2(String, SubString, 0, length(String), Index).
+	sub_string_search_2(String, SubString, 0, length(String),
+		length(SubString), Index).
 
 	% Brute force string searching.  For short Strings this is
 	% good; for longer strings Boyer-Moore is much better.
 	%
-:- pred sub_string_search_2(string::in, string::in, int::in, int::in,
+:- pred sub_string_search_2(string::in, string::in, int::in, int::in, int::in,
 		int::out) is semidet.
 
-sub_string_search_2(String, SubString, I, Length, Index) :-
+sub_string_search_2(String, SubString, I, Length, SubLength, Index) :-
 	( if
 		I < Length,
-		string__prefix(String, SubString)
+		% XXX This is inefficient --
+		%     there is no (in, in, in) = in is semidet
+		%     mode of string__substring, so this ends up
+		%     calling the (in, in, in) = out mode and then
+		%     doing the unification.  This will create a lot
+		%     of unnecessary garbage.
+		string__substring(String, I, SubLength) = SubString
 	  then
 	  	Index = I
 	  else
-	  	sub_string_search_2(String, SubString, I + 1, Length, Index)
+	  	sub_string_search_2(String, SubString, I + 1,
+			Length, SubLength, Index)
 	).
 
 %-----------------------------------------------------------------------------%

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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